Microsoft Word atn 3 2008 L10 H&F. doc

Smart Antennas

Digital beam-forming algorithms are designed to target source locations in a noisy environment. They rapidly compare responses of several spatially deployed antennas; the result of the computation is a signal that is believed to have originated from the target direction. Basically, they compute a correlation function that compares the signals and gives a measure of how close the desired and received signals are. Due to the many factors involved in the algorithm, and their wide dynamic range, floating point multiply accumulate operations are used almost exclusively to minimize roundoff errors. The target is mobile, and could be moving at a significant speed, this adds another dimension of complexity to the computation.

Manuscript received September 1, 2008; revised October 5, 2008

Figure 1. The GSM Mobile station

Figure 2. The base Station

Adaptive beam-forming makes use of additional information to continually track the mobile target. Beam-forming in 3G systems may be integrated with the Rake receiver, where the signal is operated on to combat fading and multipath effects. For these algorithms, the TigerSHARC’s rapid performance of floating-point computations makes it an excellent fit.
Smart antennas are being regarded by many as the key solution to increasing the spectral efficiency and improving the system performance in mobile communication. In principle, an antenna is smart only when it can recognize and track the signal of a particular mobile telephone while suppressing interfering signals.
Power Control: In the code-division multiple-access (CDMA) systems proposed for 3G, base-station-initiated power control of remote-unit transmitters (uplink) is critical to compensate for fast fading, peaks in transmission power, and to avoid near-far problems3. This is necessary to reduce inter-cell interference. The computations required for power control are multiply-accumulate intensive, requiring high performance digital signal processing to meet delay time requirement in 3G systems. Base stations may also implement the feedback mode transmit diversity (FMTD) algorithm, which is a power control/beam forming application that uses multiple antenna transmissions with varying weights. The computation is multiply-accumulate intensive. For such applications, ADSP-21065L SHARC is a processor of choice.